Decorated substrates such as walls, ceilings, countertops, and furniture are widely used for commercial and residential applications. An example of a method of applying decorative design to substrates is the use of sublimation dyes. This method of decorating involves printing a design on a transfer sheet using sublimation dyes, and transferring the design from the transfer sheet to the substrate by the application of heat and pressure.
In the thermofusion process of manufacturing laminates, decorative sheets are saturated with reactive resins, which are partially cured at the point of manufacture. Final curing is done at the time of hot press lamination, when the resin forms a hard cross-linked thermoset material. These products are self-bonding, that is, the resin in the decorative sheet flows into the surface of the substrate during the lamination to form a permanent bond.
Two different resin systems are presently used to impregnate substrates with resin for use during lamination. In the first system known as thermofused melamine (TFM), melamine is introduced into the substrate during an impregnation process. After the substrate is impregnated, it is partially cured in a curing oven. The melamine resin is fully cured at 300-400 psi and 300-400° F. during hot press lamination. A drawback to this process is that the resultant melamine-impregnated substrate has a finite shelf life that decreases with increased temperature and humidity.
The second resin system employs a polyester resin known as thermofused polyester (TFP), which is similarly introduced into the substrate during an impregnation operation. The substrate is heavily impregnated with polyester resin in a dip tank and then partially cured at 140 psi and 300-370° F. during the press lamination step.
The TFM manufacturing processes and resultant thermofused products can have disadvantageous properties. For example, products containing thermofused melamine such as melamine phenolic resins are disadvantageous at least from an environmental standpoint.
Water-based acrylate resins have been typically used to impregnate a single layer of a fibrous substrate, for example, the manufacturing of interior side panels for automotive parts that are then wrapped with leather or vinyl. However, it has not been previously known to bond at least two plies of a natural material using water-based synthetic resins such as acrylate resins to obtain continuous backer sheet thermofused laminates.
There is, therefore, an unmet demand for methods of preparing continuous thermofused backer sheet laminates which have little or no volatile organic content (VOC) and which do not release formaldehyde, and which have the performance attributes of TFM and TFP.